On 2013-02-11 15:21:13 +0100, Boszormenyi Zoltan wrote: > 2013-01-24 18:02 keltezéssel, Tom Lane írta: > >Andres Freund <and...@2ndquadrant.com> writes: > >>On 2013-01-24 11:22:52 -0500, Tom Lane wrote: > >>>Say again? Surely the temp file is being written by whichever backend > >>>is executing SET PERSISTENT, and there could be more than one. > >>Sure, but the patch acquires SetPersistentLock exlusively beforehand > >>which seems fine to me. > >Why should we have such a lock? Seems like that will probably introduce > >as many problems as it fixes. Deadlock risk, blockages, etc. It is not > >necessary for atomicity, since rename() would be atomic already. > > There is a problem when running SET PERSISTENT for different GUCs > in parallel. All happen to read the same original file, and only one > setting ends up in the result if you rely only on the rename() being atomic. > The LWLock provides the serialization for that problem.
Tom was voting for one-setting-per-file, in that case the problem doesn't exist. Greetings, Andres Freund -- Andres Freund http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
